Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 5/12/2006
Publication Date: 6/14/2006
Citation: Yokomi, R.K., Mello, A., Fletcher, J., Chen, J.C. 2006. Identification of infection loci of Spiroplasma citri in the San Joaquin Valley. Phytopathology 97:S172. APS Net. 2006 Pacific Division Meeting Abstracts, June 13-16, 2006 - Boise, ID. Posted online Oct. 2, 2006. http://www.apsnet.org/ meetings/div/pc06abs.asp.
Technical Abstract: Spiroplasma citri, a phloem-limited, Gram positive prokaryote lacking a true cell wall, is the causal agent of citrus stubborn disease. The vectors of S. citri in California are leafhoppers and includes Circulifer tenellus and Scaphytopius spp. The purpose of this research is to survey citrus and other known hosts of S. citri to determine the incidence, distribution and economic impact of the pathogen in California. Detection of S. citri was based on isolation and culturing in vitro and examining the cultured microorganism by dark field microscopy. Lyophilized or silica gel-desiccated sample tissue was tested by PCR using spiralin gene primers. PCR detection was reliable when S. citri titer was high in warm weather but was not reliable during late fall and winter when titer and pathogen distribution were low or erratic. DNA extraction and purification improved PCR detection but made large-scale sample processing laborious and costly. Immunocapture PCR was developed using S. citri polyclonal antiserum. The modified PCR protocol improved detection sensitivity 104- to 105-fold and will be used in future surveys. Field samples were collected from July to December 2005. S. citri was readily detected in symptomatic citrus trees in Tulare and Kern Counties and was also found in daikon (Fresno Co.) and carrot (Fresno and Kern Counties) showing symptoms of purple top. Surveys for S. citri will continue in citrus and other potential hosts in various regions of California in 2006 and 2007.